The invention relates to the use of carboxylate salt compositions in the dyeing of textile materials. Large quantities of salt are required in the process of dyeing cellulosics in order to exhaust the dyes onto the textile materials. Salt requirements vary depending upon the type of dye and dye procedure, with direct dyes requiring substantially less salt than reactive dyes. Conventionally, both direct dyes and reactive dyes are used in an aqueous bath in the presence of a neutral salt, which is typically sodium sulfate (Glauber's salt) or sodium chloride. During this stage, the dye is absorbed by the fabric as the result of a "salting out" effect from the added salt. For reactive dyes, the salting out step is followed by a reaction step in which alkaline material is added to promote a covalent bond between the dye and the fabric.
In a conventional dyeing operation, the required amount of salt increases as the depth of shade moves from the pastel/light to the dark range. Direct dyes ordinarily require about 2.5 to about 7.5 grams (g) per liter (L) for light shades, about 7.5 to about 12.5 g/L for medium shades, and about 12.5 to about 20 g/L for dark shades. Fiber reactive dyes require amounts 5 to 10 times higher than direct dyes, with ranges of about 30 to about 60 g/L for light shades, about 60 to about 80 g/L for medium shades, and about 80 to about 100 g/L for dark shades. The large quantities of salt in the dyeing process result in large quantities of salt in dye house wastewater that usually ranges from tpproximately 2,000 ppm to approximately 3,000 ppm. The large quantities of salt used in the dyeing of cellulose textile materials combined with a growth of cotton in the U.S. apparel market has resulted in increasing environmental concerns. The salt output from the textile industry can produce toxic effects on freshwater organisms due to increased salinity of the water. The environmental problems associated with large quantities of chloride in the water have resulted in regulatory limits on textile plant wastewater which start at 250 ppm of chloride. Although sulfate in the water is not currently regulated per se, increased salinity of wastewater due to the use of large amounts of sodium sulfate in the dyeing process is a significant concern. Additionally, wastewater containing large amounts of dissolved salts has been identified as contributing to decreased efficiencies of wastewater treatment plants as the result of the high amount of dissolved solids.
Various strategies have been employed or suggested for reducing the salt content in textile mill effluent that is attributable to the dyeing process. These include the development of new dyes which require less salt, the recycling of dyebaths, and the derivatization of cotton to make it cationic. Although the development of new dyes which require less salt has some potential for alleviating the salt requirementsjn the dyeing process, this is a long-term project and only a partial solution to the problem because salt requirements will be reduced but will still remain substantial. Additionally, revamping entire dye lines will take considerable time in research and development and in commercial translation. Derivatization of cotton so that less salt is required in the dyeing process has resulted in non-uniformity in the dyed product. Problems associated with dyebath reuse include the cost and the risk of a dirty dyeing procedure which adversely affects the dyeing of the fabric and results in dirty equipment, the eventual generation of chlorine or nonbiodegradable salt in the wastewater, and excessive waste.
In U.S. Pat. No. 5,207,800 (hereinafter "the '800 patent"), the use of alkaline earth metal organic salts for replacing sodium salts in dyeing cotton fabrics is disclosed. In particular, the '800 patent discloses the use of magnesium salts of organic acids. The '800 patent does not disclose or suggest the use of organic acid salts wherein the cation is something other than a bivalent alkaline earth metal, such as the monovalent alkali metals of sodium or potassium. The '800 patent discusses the importance of using alkaline earth metals salts, which have a lower solubility in water than sodium salts, so that the alkaline earth metals can be removed by precipitation during treatment of wastewater from the dyeing process. The '800 patent described the results as excellent with direct dyes and problematic with reactive dyes.